Thermostatic switch



Aug. 9, 1955 c. s. MERTLER THERMOSTATIC SWITCH Y 2 Sheets-Sheet 1 FiledJuly 25, 1950 HG. i

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c. s. Ml-:RTLER 2,715,167 THERMOSTATIC swTcH 2 Sheets-Sheet 2 Aug. 9,1955 United States Patent() pas THERMSTATIC SWITCH Charles S. Mer-tier,Mansfield, Ohio, assignor to Stevens Manufacturing Company, Inc.,Lexington, Ohio, a corporation of Ghio Application `luly 25, 1950,Serial No. 175,696

24 Claims. (Cl. 20G-138) This invention relates to thermostatic switchesand more particularly to temperature responsive switches which operatewith a snap action at a predetermined temperature.

An object of the invention is to provide improved thermostatic switcheswhich operate with a snap action within a very narrow temperaturedilierential thereby providing a more reliable circuit control, longercontact life, and reduced radio interference since fluttering or fryingof the contacts is substantially eliminated, the switches being capableof carrying very substantial current loads and rapidly responding tochanges in ternperature of the surface or surfaces upon which they aremounted.

Another object of the invention is to provide an improved thermostaticswitch having a very narrow temperature range or differential throughutilization of a buckling or over-center spring as one contact of theswitch, the said spring being anchored at only one end with the otherend free to snap to and from engagement with a second contact inresponse to force exerted on the spring by a thermoresponsive memberresponding to a predetermined change in temperature.

A further object of the invention is to provide an improvedthermostaticswitch as defined in the preceding paragraph and wherein a means isprovided which causes the said buckling or over-center spring to snapback to its initial position when the force exerted thereon by thethermoresponsive member is removed.

A still further object of the invention is the provision of an improvedthermostatic switch as defined in either of the two preceding paragraphsand in which the thermoresponsive member is an elongated bimetallicmember having a planar portion positioned for metallic con ductive heatexchanging relationship with a surface the temperature of which is tocontrol the said switch, there being motion transmitting meansintermediate the said bimetallic member and the said spring so that theiiexing of the former operates the latter.

An additional object of the invention is to provide an improvedthermostatic switch as defined in the preceding paragraphs and in whichthe motion transmitting means applies the force exerted by saidbimetallic member upon said spring with a mechanical advantage.

A still further object of the invention is to provide an improvedthermostatic switch employing an overcenter or buckling spring as one ofthe contacts thereof, the said spring being actuated by liexing of thecentral portion of a bimetallic member, which member has the endsthereof slidingly supported in heat exchanging relationship with thesurface whose change of temperature effects flexing of the said centralportion.

It is also an object of the invention to provide a thermostatic switchas defined in any of the preceding objects and further provided withmeans to readily select the predetermined temperature at which theover-center or buckling spring is operated by the thermoresponsivemember.

Ll il ICC The invention further resides in certain novel features ofconstruction and combination and arrangements of parts, and furtherobjects and advantages thereof will be apparent to those skilled in theart to which the invention pertains from the following description ofthe present preferred embodiment thereof, and certain modifications,described with reference to the accompanying drawings in which identicalparts in the several views are designated by the same referencecharacters and in which:

Fig. l is a top plan view of the present preferred embodiment of athermostatic switch incorporating the novel features of this invention;

Fig. 2 is a longitudinal sectional view through the switch illustratedin Fig. 1, the view being taken approximately on the line 2 2 of Fig. lwith portions of the operating mechanism shown in elevation to moreclearly illustrate the construction;

Fig. 3 is a bottom View of the embodiment of the switch illustrated inFigs. l and 2;

Fig. 4 is a detached elevational view of the over-center or bucklingspring utilized in the switch illustrated in Figs. l-3;

Fig. 5 is a longitudinal sectional View through a modified form ofthermostatic switch embodying the invention, portions of the operatingmechanism being shown in elevation to more clearly illustrate theconstruction;

Fig. 6 is a detached elevational View of a modified form of over-centeror buckling spring which may be employed;

Fig. 7 is a longitudinal sectional View through Still another form ofthermostatic switch embodying the invention, portions of the operatingmechanism being shown in elevation to more clearly illustrate the con-kstruction;

Fig. 8 is a longitudinal Sectional View through yet another form ofthermostatic switch embodying the invention with portions of theoperating mechanism shownl in elevation to more clearly illustrate theconstruction; and

Fig. 9 is a detached elevational view of another manner of forming anover-center or buckling spring which may be utilized in the novelswitches, the form of spring here shown being that illustrated asincorporated in the switches shown in Figs. 7 and 8.

The thermostatic switches of this invention are of the snap action type.That is to say, upon attainment of a predetermined operating temperaturethe contacts of the switches move from one position to the otherrelatively rapidly, or with a snap action, thereby preventingfluttering, frying and similar diliiculties which are present inthermostatic switches of the creep type. Heretofore, it has beencustomary to employ relatively complicated mechanisms to effect thissnap action, but, in accordance with this invention, the desiredsnapping of the contacts is effected through the utilization of a singlespring member thus eliminating many of the parts heretofore deemednecessary for snap acting switches consequently reducing the cost whileat the same time providing a more reliable operation.

The spring element employed in the switches of this invention is forconvenience hereinafter referred to as an over-center or buckling typespring. Such a spring may be formed in a variety of dilferent mannersbut in the preferred embodiment the spring is of the type illustrated inFig. 4. As shown therein the spring, generally designated 1l), comprisesan elongated piece of relatively thin spring material such as temperedsteel, brass, phosphor bronze, or the like. This strip of material 10 islongitudinally slotted or slit, as indicated at 11 and 12, parallel withthe longitudinal edges of the strip but with the ends of the slots orslits entirely enclosed within the edges of the spring. There is thusprovided a central portion A and outer portions B and C of the springwhich are all parts of the integral strip. The central portion A of thespring is elongated with respect to the side portions B and C so thatthe spring tends to assume a curved configuration, as viewed in sideelevation, the direction of curvature depending upon whether the centralportion A is disposed to one side or the other of the plane of the sideportions B and C. When the central portion A is disposed to one side ofthe plane of the side portions B and C, the said central portion may bereadily caused to snap through center to the other side of the plane ofthe portions B and C by application of a force to the said centralportion. Because the central portion can never lie exactly in the planeof the side portions B and C but must always buckle or snap to passbeyond the center line or plane of such portions, the spring is said tobe of the over-center or buckling type.

In order to provide the difference in lengths between the central andside portions of the spring, the latter, in the form shown in Fig. 4,has had the side portions B and C reduced in length by crimping orcreasing them intermediate the ends of the spring as indicated at 13 and14. The difference in length between the central and side portions ofthe spring can also be achieved by stretching the central portion withrespect to the side portions. Such a construction is shown for thespring member illustrated in Fig. 9 and generally designated 15.

As shown in Fic'. 9, the spring 15 comprises an elongated strip ofresilient ma-terial such as tempered steel, brass, or phosphor bronzewhich has been slit or slotted as indicated at 16 and- 17- parallel withthe longitudinal edges` of the spring to provide the central portion Aand the side portions B and C', the ends of the slits or slots 16, 17being entirely enclosed within the edges of the spring. The constructionin this respect is therefore identical to that shown. in Fig. 4. In thisform of the spring, however, the central portion A is stretched whilethe side portions B and C are not thus treated so that the centralportion is againof greater length than the side portions just as in thecase of the spring shown in Fig. 4. Consequently, the central portion Ais buckled or bowed to one side of the plane of the side portions B andC and will assume such a position to either side of the plane of theside portions with a corresponding curvature of the spring member 15 asa whole whenever the central portion A has been snapped through center.

While the two forms of the spring, shown in Figs. 4

and 9, have each been illustrated as constructed. from.

one piece of metal, it will be apparent that they may each be formed ofseveral separate pieces joined together by welding or riveting. Such aconstruction is illustrated in Fig. 6. As shown therein, the springportion 10a is constructed in the same manner as spring. 10, but of :'f

lesser length, and is riveted to a member or portion 10b whichis alsoresilient. The member or portion 10b preferably is provided with acentral tongue or prjection 16o positioned to overlap a part of thecentral or buckling portion of the spring. With a spring of this form,the actuating force may be applied to the portion or member 10b,preferably adjacent the tongue 10c, and the latter will then transmitthe force to the buckling central portion of the spring. .As indicatedabove, the portion 10a corresponds in construction with the form of thespring shown in Fig. 4. However, the portion 10a could be constructed inthe manner described for the spring illustrated in Fig. 9.

The spring members shown in Figs. 4, 6 and 9 are the same in principleand operate in the same manner in the switches and may beinterchangeably used in any of the forms of the switches hereinafterdisclosed. Therefore, while certain forms of the switches may be shownas utilizing a spring of the type shown in Fig. 4 and others asutilizing a spring formed in the manner described with respect to Fig. 9this is but for convenience and is not intended as a limitation upon theswitch constructions. Furthermore, springs having the characteristicsdened but constructed by other means than crimping the sides such as B,C or B', C or by stretching the center portion such as A or A may beutilized within the scope of this invention.

Figs. l through 3 illustrate the present preferred embodiment of athermostatic switch constructed in accordance with this invention andembodying an over-center or buckling spring of the type defined above.The switch herein shown is of the enclosed type comprising an oblonghousing, generally designated 18, which may be formed from sheet metalby drawing, may be cast in one piece, or may be assembled from severalparts. In the form shown, the housing 1S is illustrated as of one piececonstruction being substantially U-shaped in longitudinal sectionthereby providing a recess or cavity 19 within which the operatingportions of the switch are enclosed, the housing having outwardlyextending ears or lugs 20 and 21 by which the housing may be applied toa surface the temperature of which is to control operation of theswitch.

The top of the recess 19, as viewed in Figs. l and 2, has a pair ofterminal members 22 and 23 secured thereto in spaced relationship. Inthe form shown, these terminal members each comprise substantially rightangled brackets, the upstanding legs of which are providedk with tappedholes such as 24, 25 for the reception of screws by which conductors maybe connected to the switch. The horizontal legs of the terminals 22, 23are each apertured and are secured to the housing 18 by having aterminal post or stud 25 or 27, respectively, disposed within the cavity19 with a reduced diameter portion of each of the posts extendingthrough separate openings in the housing and the openings in thehorizontal portions of the corresponding terminal lugs 22, 23, the outerends of the terminal posts being peened over as indicated in Fig. 2.When, as in the illustrated embodiment, the case or housing 18 is formedof metal, insulation is provided between the terminal lugs 22, 23 andthe outer side wall of the housing as well as between the posts 26, 27and the inner side wall of the housing, such insulation being in theform of mica or other insulating plates 28 and EL) interposed asaforementioned, it being understood that the reduced diameter portionsof the terminal posts 2,6, 27 are of less diameter than the openings inthe housing 18 through which they extend, see Fig. 2.

The terminal post 26 is preferably of shorter length than the terminalpost 27 and the inner end of the post 26 has a reduced diameter portionpassing through an opening at one end of the over-center or bucklingspring 1G and through a corresponding opening in a relatively rigid armor stationary member 31, the lower end of the post 26 being peened overto firmly secure the spring and the arm 31 in the relationship shown inFig. 2. The arm or stationary member 31 has a raised portion 32 integralwith or attached thereto adjacent the outer end and bearing upon theportion A of the spring 10 at substantially the center thereof thusnormally preventing movement of this portion of the spring transverselyrelative to the arm 31 without, however, preventing tieXing of thespring and movement of the end thereof which is opposite the post 26.While the arm or member 31 has been defined as relatively rigid orstationary this member has sufcient flexibility to permit adjustmentthereof and hence of the switch operation as hereinafter described.

The spring 1t) has an electrical contact 33 integral with or secured tothe unslotted portion of the spring adjacent the outerV end thereof,this contact being preferably a button of silver or silver alloy.Adjacent the contact 33 the spring 10 is provided with a substantiallyU- shaped portion 34 which may be either integral with the spring, asshown, or may be a separate bracket attached thereto. This U-shapedportion 34 hasthe part or arm thereof which is spaced from the main bodyof the spring provided with an insulating button 35 of ceramic materialor the like, the purpose of which will be hereinafter described.

The lower portion of the terminal post 27 has a reduced diameter portionpassing through an opening in resilient contact arm or member 36 whicharm or member is firmly secured to the post 27 by peening the outer endof the latter over, a washer such as 37 being preferably interposedbetween the arm or member 36 and the peened outer end of the terminalpost 27 to insure proper support. rl`he arm or member 36 is resilientand is preferably biased in a direction such that its free end tends tomove away from the spring member 10. Adjacent its free or outer end thearm or member 36 is provided an electrical Contact or button 38, whichmay be silver or a silver alloy, positioned for engagement with thecontact 33 on the spring 10.

The switch is actuated by a thermoresponsive member acting upon theresilient arm or member 36 and operating through the latter to snap orbuckle the Spring 10 over-center from a position in which the contactsare engaged to a position in which they are disengaged. For this purposethe housing 18 has the end walls 39 and 40 thereof slotted adjacent theears or flanges 2l), 21 and a thermoresponsive member, which is hereshown as an elongated and substantially planar bimetallic member 41,extends the length of the recess 19 with the ends of the bimetallicmember passing through the said slots in the end walls of the housing 18and slidably supported on the ears or flanges 20, 21. To facilitate thissliding support and provide for equalization of the support, thebimetallic member is preferably provided with small rounded projectionsor feet such as 42, 43 and 44. These projections or feet are preferablyprovided by indenting or punching the bimetallic member on the sideopposite the side thereof which is to rest upon the ears or flanges 28,21. Preferably two such projections or feet are provided at one end ofthe bimetallic member and only one such projection or foot at the otherend thereof, thus effecting the well-known triangular support preventingcocking of the bimetallic member as might occur if greater or lessernumber of projections or feet were employed.

Intermediate the ends and substantially centrally thereof, thebimetallic member 41 is provided with an upstanding post 45 preferablyformed of insulating material, for example, ceramic material or thelike, which may be secured to the member 41 in any suitable manner. Theupper end of the member or post 45 has a reduced diameter portion 46which freely passes through an opening in the resilient arm or member 36the latter resting upon a shoulder 47 of the post 45 formed at the baseof the reduced diameter portion 46.

ln the preferred construction as here illustrated, the housing 1S ismade of metal and the ears or flanges 20, 21 are secured to the surfacewhose temperature is to operate the switch. Consequently, thethermoresponsive member, namely, the bimetallic strip 41, is in goodthermal exchange relationship with the surface whose temperature is tooperate the switch, this being due both to the close proximity of thebimetallic member with the surface as well as the fact that its ends arein positive metal-to-metal contact with the metallic flanges or ears 20,21 that are in turn contacting the surface whose temperature is toeffect switch operation. Therefore, the bimetallic member rapidlyresponds to changes in temperature of the surface upon which the switchis mounted and correspondingly flexes or bows intermediate its ends. Inthis exing or bowing the bimetallic member 41 is unrestrained since itsouter ends are free to slide upon the ear or flanges 20, 21 with theresult that repeated operations of the bimetallic member are always thesame for the same predetermined temperature there being no extraneousstresses introduced, as frequently happens when the bimetallic member issecured to a rigid member. Moreover, the effect of the flexing of thebimetallic member is applied to the movable contact of the switch with amechanical advantage so that a relatively small tem- ',-eraturedifferential is sufficient to effect switch operation, thus preventingthermal lag which is one of the objections to conventional thermostaticswitches. rIhat is to say, when the bimetallic member iiexes, the postor member 45 moves upwardly as viewed in Fig. 2 thereby moving theresilient arm or member 36 upwardly and applying the force exerted bythe bimetallic member through the contact 38 to the contact 33 on thespring member liti. Therefore, the force exerted by the bimetallicmember is applied with the mechanical advantage provided by the arm 36so that a relatively small deflection of the bimetallic member iseffective to provide an amplified movement of the contact 38.

The force exerted upon the contact 33 by the contact 38, as the resultof flexure of the bimetallic member 41, causes the spring 10 to snap orbuckle through center so that it tends to assume a curvature in adirection reverse to that shown in Fig. 2 and this effects separationbetween the contacts 33 and 38 since it will be remembered that theresilient arm 36 is biased in a direction tending to maintain the latterin engagement with the post 45 and hence does not follow the contact 33except to the extent required by the button 35 which now engages the arm36. Since the spring 10 is of the buckling or overcenter type, movementof the contact 33 from engagement with the contact 38 is effected with asnap action so that there is an abrupt change from contact engagement tocontact separation, thereby preventing fluttering and frying of thecontacts Stich as occur when the movable contact of a switch remains foran appreciable time in an unstable central position with respect to thestationary contact. As a matter of fact the contact pressure just priorto contact separation is increased in switches constructed in accordancewith this invention whereas in conventional switches the Contactpressure continuously decreases as the operating temperature is reached.

T he purpose of the U-shaped portion 34 and the insulating button 35 onthe spring 10 is to limit the amount of contact separation therebyreducing the temperature differential required for reclosing of thecontacts. Thus, when the spring 10 is buckled or sprung past center, thecontact 33 moves from engagement with the contact 38 but the extent ofthis separation is limited by engagement of the button 35 under the endof the resilient arm 36. In addition to limiting the extent ofseparation, the resiliency of the arm 36 acts through the button 35 torestore the spring 10 to its initial position upon removal of theactuating force exerted by exing of the bimetallic member 41. That is tosay, since the resilient arm 36 tends to remain in engagement with thepost 45, straightening of the bimetallic member 41 in response todecrease in temperature of the surface adjacent the bimetallic 1 member,causes the resilient arm 36 to follow the post 45 thereby exerting forceon the button 35 thus causing the spring 10 to snap back through centerto its initial bowed or curved position in which the contacts 33 and 38are in engagement.

To further control the operation of the switch and restrict the contactoperation to a relatively narrow temperature range or differential, thecentral portion A of the spring 1t) is, as previously described, engagedby the projection or button 32 on the arm 31. The other side of thecentral portion A of the spring 10 is engaged by an abutment member 48.Hence, the outer end of the spring 10, carrying the contact 33, mustsnap through the center position upon a relatively small movement of thesaid outer end of the spring since the central portion A thereof isconfined between the members 32 and 48 and hence cannot crinkle orotherwise deform and leave the spring in an unstable middle position.

The abutment or member 48 is preferably formed of porcelain or otherinsulating material and provided as an insert in an adjusting shaft orscrew 49 which is threadedly mounted in a tapped bushing or collar 50supported upon the case or housing 18 substantially above the centralportion f the spring 10. The outer end of the shaft or screw 49 may beprovided with any suitable form of knob, not shown, for actuating thelatter and the shaft intermediate its ends may be provided with aprojecting lug such as 51 for cooperation with an upstanding lug S2 onthe collar 50 to thereby limit the extent of adjustment of the shaft orscrew 49. It will be evident therefore that adjustment of thepredetermined temperature at which the switch operates may be selectedby adjustment of the screw or shaft 49. In this connection it should benoted that while the arm 31 is substantially rigid and stationary it hassuicient resilience to tend to move upwardly when the force exerted bythe shaft 49 is reduced by retraction of the latter. That is to say,when the screw or shaft 49 is retracted its maximum extent the button orportion 32 on the arm 31 will still maintain the central portion A ofthe spring 10 in engagement with the insert 48 of the adjusting screw orshaft 49 and the contacts 32 and 3S will remain engaged. However, agreater movement of the contact 38 is now required to snap the spring1li through center and hence a higher ternperature is needed forproducing sufficient deiiection to effect contact separation.Conversely, adjustment of the screw or shaft 49 downwardly will requirea lesser deflection and hence a lower temperature of the bimetallicmember 41 to cause snapping of the spring 1t) over-center withconsequent switch operation. ln all cases, however, the extent ofcontact separation when the switch is opened in substantially the sameso that the temperature differential between the open and the closedpositions of the switch contacts is not varied by the predeterminedtemperature at which switch operation is effected.

While the switch shown in Figs. l-3 is illustrated as being of theclosed type, it will be readily apparent that the same mode of operationwill be effected with an open type switch. In such a construction thesupport for the operating portions of the switch is provided by asubtiel:- tially U-shaped bracket having open sides rather than theclosed sides provided by the housing 18 illustrated. The operation ofthe switch is not varied, however. The housing 18, or its equivalent, aU-shaped bracket, is preferably metallic to provide good heat exchangebctween the bimetallic member 41 and the surface on which the switch ismounted. However, in some cases, the housing l or equivalent bracket maybe formed of plastic or other material. lt should also be noted that,while the bimetallic member or strip 41 has been shown as of greaterwidth adjacent the middle than at either end, this is not essential andthe strip may be substantially rectangular or of other configurations ifdesired. Moreover, in its broader aspects the invention includesoperation of the arm 36 by a thermoresponsive means other than abimetallic member, the force of which would be applied through a pin orpost such as 45 shown in Fig. 2.

Figs. and 6 show a modified form of switch embodying this invention andemploying the buckling or overcenter spring similar to that shown inFigs. 1 4. This embodiment of the switch is likewise shown as being ofthe enclosed type comprising a housing 53 identical with that designated1S in Fig. 2. ln the instant form the switch is likewise provided withterminal lugs such as 54 and 55 secured to terminal posts 56 and 57 withinterposed insulation such as 58 and 59, these parts being identicalwith the corresponding elements 22*29 in the form of the switch shown inFig. 2 and hence need not be described in detail.

The lower portion of the terminal post 57 is provided with anover-center spring 60 which is substantially the same as the springexcept that it is not provided with the U-shaped bracket 34 at the endthereof as is the spring 1d. The spring 60 is mounted adjacent one endthereof upon the post 57 in the same manner as is the spring 10. Abovethe Vcentral portion of the spring is a 3 resilient arm 61 engaging aprojection or hump 62 on the central portion of the spring 66 andapplying a resetting force thereto thereby normally maintaining thespring 6i) in the illustrated position.

The outer end of the spring is provided with a contact 63 which isnormally engaged with a contact 64 carried upon a relatively rigid armor member 65, the other end of the latter being secured to the post 56in the same manner as the arm 36 is secured to the post 27. The outerend of the arm 65, adjacent the contact 64 is provided with a U-shapedportion 66, here shown as integral with the arm 65 and having a legextending beneath the free end of the spring 6i), this end of theU-shaped portion 66 being provided with a button or insert 67 of ceramicmaterial or the like adapted to be engaged by the end of the spring 60when the latter snaps to its other position. The bracket or portion 65therefore limits the extent of movement of the free end of the spring 60thereby reducing the temperature differential of the switch operation.

In the form of the switch shown in Fig. 5, the spring 6d is actuated toeffect separation of the contacts 63 and 64 by means of a bimetallicmember 68 of the type shown in Figs. l-3 the ends of which extendthrough slots in the vertical legs of the housing or support 53 and areslidably supported upon the horizontal ilanges or feet of the housing orsupport 53 by projections or dimples 69. Consequently, the bimetallicmember 68 is positioned so as to be directiy affected by changes oftemperature of the surface upon which the switch is mounted. Also,temperature changes of the surface are further communicated to thebimetallic member 68 through the metal-tometal Contact of both ends ofthe latter with the housing 53 which, as previously mentioned, ispreferably secured to the surface whose temperature is to control theswitch.

intermediate its ends, the bimetallic member 68 is provided with amotion transmitting element or button 70 which may be formed of ceramicor other insulating material and engages the central portion of thespring 6@ in the dimple beneath the projection 62. Consequently, whenthe thermal responsive member 68 exes in response to a predeterminedchange in temperature, this movment is transmitted to the centralportion of the spring 60 snapping the latter through center and thusseparating the contact 63 from the Contact 64 with a snap action.

The temperature at which this contact separation is effected ispreselected by means of an adjusting screw or shaft 71 which isthreadedly received within a collar or nut 72 secured to the housing thelower end of the screw or shaft 71 being provided with an insert 73 ofceramic or other insulating material engaging the arm 65. The adjustingscrew or shaft 71 preferably has a stop lug '74a for cooperation with astationary lug or projection 74b to thereby limit the extent ofadjustment of the screw or shaft 71. The arm 65 which is substantiallyrigid has, however, an upward bias and suiiicient flexibility to followthe pin or insert 73 as the latter is moved upwardly due to rotation ofthe screw or shaft 7i.. Consequently, adjustment of the switch operationis easily and simply effected by rotating the screw 71.

ln the normal position of the switch, the parts are disposed as shown in5 with the Contact 63 on the spring 66 in engagement with the contact 64on the arm 65. Upon a predetermined change of temperature, however, thebimetallic member 68 iiexes or bends with the result that its centralportion moves upwardly causing the abutment or motion transmittingelement 7i) to move the central portion or spring 60 and the arm 6lupwardly. This causes the spring 6d to buckle or snap through center, aspreviously described with respect to the form of the switch shown inFig. 2, thereby separating the Contact 63 from the contact 64, theextent of separation being determined by the width between the two sidesor legs of the U-shaped portion 66, since the arm 65 is substantiallyrigid when once adjusted. So long as the temperature remainssufficiently elevated to maintain the bimetallic member 6b exed orcurved, the spring 60 will be held in its actuated position so that thecontacts 63 and 64 remain separated. When, however, the ternperature ofthe surface on which the switch is positioned drops below thepredetermined value for which the switch was adjusted, the bimetallicmember 68 will again straighten so that the portion or abutment 70returns to the position shown in Fig. 5. The resilient arm or member 61holds the central portion of the spring in contact with the motiontransmitting abutment or button 70 and follows the latter with theresult that the spring 60 is snapped back through its central positionto its initial position as shown in Fig. reengaging the contacts 63 and64.

Fig. 7 illustrates a further modified form of the switch constructed inaccordance with this invention and cornprises a housing or substantiallyU-shaped bracket member 75, substantially identical with that shown inFigs. l-3, with openings or slots adjacent the lower portions of the endwalls thereof through which the ends of a bimetallic member 76 extend,this member being identical With that illustrated in Figs. l, 2, 3 and5. The bimetallic member 76 is provided with a motion transmittingelement 77 which may be identical with the member 45 shown in Fig. 2 butneed not be formed of insulating material. In the instant form of theswitch, however, the transmission of the movement of the birnetallicmember to the spring for effecting switch operation is provided througha lever rather than through the resilient contact arm 36 as in theswitch shown in Fig. 2. Consequently, in the instant form of the switchthe adjusting shaft 78, which is constructed in the same manner as theshaft 49, has an extension 79 the lower end of which has a reduceddiameter portion 80 extending through an opening in the outer end of alever 81 thereby providing a pivot for the lever. Intermediate its endsthe lever 81 has an opening in which is received the reduced diameterportion S2 of the motion transmitting element 77 provided on thebimetallic member 76, the other end of the lever 31 being provided withan abutment or switch actuating button or member 83 preferably formed ofceramic or other insulating material.

In the form of the switch shown in Fig. 7, the terminal lugs 84 and 85are identical with the lugs in the other forms of the switches but theterminal post 86 in the instant form of the switch has the lower endthereof silver-plated or otherwise provided with a contact surface 87thus directly forming one contact of the switch. lntermediate thiscontact surface 87 and the interior side of the top wall of the housingor bracket 75 is provided a U-shaped bracket 88, this bracket beinginsulated from the terminal post 86 and from the housing 75 byinsulation such as 89, 90 and 91, which may be sheets of mica or otherinsulating material. The terminal lug 85 is secured in place by aterminal post 92 which has a reduced diameter portion passing throughthe insulation 90, 91 with the outer end of kthis reduced diameterportion peened over the horizontal portion of the terminal lug S5 asindicated in Fig. 7. The lower portion of the terminal post 92 islikewise of reduced diameter and has mounted thereon, in verticallyspaced relationship, a relatively rigid arm or member 93 and anover-center or buckling spring generally designated 15. The spring 15and arm 93 are suitably spaced by a washer or washers 95, the assemblybeing secured by peening over the lower end of the terminal post 92. Thespring 15 is of the same general type as those designated or 60 in theprevious forms of switches but is of shorter length as will be seen fromFig. 9. As mentioned heretofore, the spring is shown as having beenformed by stretching the central portion A rather than by crimping orotherwise shortening the side portions B' and C. The method ofconstructing the spring 15 is, however, immaterial and the spring may bemade in the same manner as the springs 10 and 60. The free end of thespring 1S is provided with the conl0 tact member 96 which is normally inengagement with the contact surface 87 as shown in Fig. 7.

In the instant form of the switch it will be observed that the arm 93extends above the spring 15 and has a button or downwardly extendingportion 97 engaging the central portion A' of the spring 15 adjacent anend of this central portion, namely, near the ends 0f the slots such as16, 17, while the ceramic button or motion transmitting element S3 onthe lever 81 is substantially directly below this portion of the spring.

It will be apparent that in the switch shown in Fig. 7, a change oftemperature causes the bimetallic member 76 to flex thereby moving thecentral portion 77 thereof upwardly which acts through the lever 81 toamplify this movement, causing the button or member 83 to engage thespring 15 and snap or buckle the latter through center, therebyreversing its curvature from the position shown in Fig. 7. Movement ofthe outer end of the spring 15 is limited by the lower arm or portion ofthe bracket 8S while the upward bowed position of the central portion ofthe spring is limited by the button 97 of the arm 93. This arm 93 andits button 97 are so positioned that the central portion A' of thespring 15 cannot assume a stable position of reversed curvature but willremain in the position holding the contacts S7 and 96 separated so longas the member S3 exerts force upon the spring by the exed or deectedportion of the bif metallic member 76. When, however, the temperaturechanges so that the bimetallic member returns to its initial position,namely, that shown in Fig. 7, the lever 81 will, due to the weight ofthe member 83 and the force exerted by the spring 15, return to itsinitial position and as the abutment or button 83 thus retreats thespring 1S will snap back to its initial position, namely, to theposition in which the contacts are in engagement as shown in Fig. 7.

In the form of the switch shown in Fig. 7 adjustment is effected as inthe other forms by simply varying the position or adjustment of theshaft 78 as will be readily apparent. Moreover, it will be apparent thatin place of the substantially closed housing 75 here illustrated an openmounting member may be employed for the switch elements which mountingmember may be substantially U-shaped similar to the cross section of thehousing 75.

Fig. 8 illustrates still another form of switch embodying thisinvention. In this form of the switch the terminal lugs 98, 99 andterminal posts 100, 101 are the same as the terminal lugs 84, and theterminal posts 86 and 92. Likewise, the terminal post 100 is providedwith a contact surface 102 and a bracket member 103 identical with thecontact 87 and bracket 88 in Fig. 7, insulation 104, 105, 106 beingprovided in the same manner and for the same purpose as insulation 89,and 91 of Fig. 7. Likewise, the terminal post 101 is provided with asubstantially rigid arm 107 having a button or portion 108 cooperatingwith a spring member 109, these parts corresponding with the identicalparts 93, 97 and 15 in Fig. 7. The spring 109 has a contact 110 normallyengaged with the contact 102 as in the previously described switch.

Likewise in the form of the switch shown in Fig. 8, an adjusting screw111 is provided which operates in the same manner as the otherpreviously described adjusting screws except that the lower portionthereof is provided with an insert 112 of insulating material such asceramic or the like which bears upon a bimetallic member 113intermediate the ends of the latter. In the form of the switch shown inFig. 8 the bimetallic member is substantially L-shaped and has theshorter leg or portion thereof united with an end wall of the housing ormounting bracket 114 by screws, rivets, welding, brazing or the like.The main portion of the bimetallic member is planar and extendsthroughout the major portion of the length of the housing or bracket 114closely adjacent the bottom thereof so as to be directly effected by l lchanges of temperature of the surface upon which the switch is mounted,temperature changes of the surface also being communicated to thebimetallic member 113 through the inetal-to-metal contact of the latterwith the support or housing 1M. rfhe free end of the bimetallic member113 is providedl with a motion transmitting means, such as a button orpin 115 of insulating material, which engages the central portion of thespring 109 directly beneath the portion thereof which is engaged by thebutton or projection 108 on the arm M7.

The operation of the switch shown in Pig. 8 is substantially like thatpreviously described for the switch shown in Fig. 7 except that there isno amplification of the movement of the bimetallic member. Operation ofthe spring 109 to and from engagement with the stationary contact 102is, however, the same as the operation of the spring 15 to and fromengagement with the Contact 87 in the form of the switch shown in Fig. 7and hence a description thereof need not be repeated. Adjustment of thetemperature at which switch operation is effected is accomplished byvarying setting of 'the screw or shaft 11.1 as in the other forms of theswitch.

it will now be apparent from the foregoing description and theaccompanying drawings that this invention provides thermostatic switchesof the snap acting type which are relatively simple in construction yetreliable in operation and which require a smaller temperaturedifferential for effecting operation than do conventional snap actingswitches. This is due to the fact that the overcenter or buckling springis not rigidly secured at both ends as is customary where such springshave been utilized heretofore, but, on the contrary, the spring issecured at one end with the other end free to move and effect thecontact operation. Moreover, the extent of contact separation iscarefully regulated so that repeated switch operations may be effectedwithout an appreciable variation in the temperature differential of theswitch. Furthermore, the construction of the switches is such that thethermoresponsive members may be closely disposed adjacent a surface, theheat of which is to effect switch operation, the thermoresponsivemembers also being in good thermal contact by virtue of their mountingsin metal-to-metal contact with the housings or mounting brackets, itbeing remembered, as mentioned heretofore, that when an open type switchis desired, the mounting therefor need not be a housing but may besimply a bracket having open sides. The thermal exchange from thesurface upon which the switch is mounted to the bimetallic member isespecially good in the form of the switches shown in Figs. 2, 5 and 7wherein both ends of the bimetallic member are in metal-tometal contactwith the housing or bracket resting upon the surface whose temperaturevaries so that both ends of the bimetallic member are equally effectedby temperature changes.

While the invention has been described in very considerable detail inorder to comply with the requirements of the statutes to fully disclosethe invention, it will be appreciated that variations may be made in thedetails of construction and the position and arrangement of partsWithout departing from the essence of the invention. Thus, while theswitches have been shown as having the contacts thereof normally engagedand operated to disengaged positions in response to flexing of thebimetallic members, the reverse operation can be readily effected sothat the contacts are normally open but are closed at a predeterminedtemperature in response to flexing of the bimetaliic member. Also, inthe forms of the switches similar to those shown in Figs. l through 5,the spring member, arm member, etc., may all be mounted upon a singlepost rather than upon two separate posts as illustrated. Moreover, abimetallic member rigidly mounted at one end, similar to that shown inFig. 8, may be employed with the switch constructions shown in Figs. lto 3, 5 and 7, if desired, in place of the bimetallic membersillustrated therein. These and other changes can be readily effected bythose skilled in the art and hence the detailed drawings anddescriptions are intended simply as illustrating practical embodimentsof the invention and are not to be considered as limitations thereonexcept as required by the spirit and scope of the appended claims.

Having thus described the invention, I claim:

l.. An electrical switch comprising an over-center spring, meanssupporting said spring at only one end thereof, means providing anelectrical contact on said spring adjacent the other end thereof, aSecond electrical contact supported for engagement by thefirst-mentioned Contact, an elongated non-stressed biinetallic memberhavinga planar portion adapted to ex relative to said spring in responseto changes in temperature, means supporting said bimetallic member innon-stressed condition and in a position for good heat exchangerelationship with a surface subject to variations in temperature, motiontransmitting means intermediate the said planar portion of thebimetallic member and said spring exerting force upon the latter whenthe said birnetallic member iiexes a predetermined amount therebysnapping said spring over-center to effect movement of the contactthereon relative to said second contact, and means acting on said springto effect automatic resetting of the latter to its initial positionafter flexure of said bimetallic member has been reduced below saidpredetermined spring-operating amount.

2. An electrical switch as defined in claim l and further comprisingmeans to adjust said switch for contact operation at differentpredetermined temperatures.

3. An electrical switch comprising an elongated overcenter spring havinga central portion of dierent length than the sides thereof therebycausing said spring to snap through a central position upon applicationof force thereto, means supporting said spring at only one end thereof,means providing an electrical contact on said spring adjacent the otherend thereof, a second electrical Contact suo` ported for engagement bythe first-mentioned contactfa thermoresponsive member having a portionadapted to move relative to said spring in response to changes intemperature, means supporting said thermoresponsive member innon-stressed condition for mounting adjacent to and in metal-to-metalheat exchange relationship with a surface subject to variations intemperature, motion transmitting means intermediate saidthermoresponsive member and said spring exerting force upon the latterwhen the said thermoresponsive member moves in one direction therebysnapping said spring over center to effect movement of thefirst-mentioned Contact relative to said second contact, and meanscausing said spring to automatically snap back to its initial positionupon restoration of said thermoresponsive member to substantially itsinitial position.

4. An electrical switch comprising an elongated overcenter spring havingintegral central and side portions of different lengths thereby causingsaid spring to snap through a central position upon application of forcethereto, means supporting said spring at only one end thereof, meansproviding an electrical contact on said spring adjacent the other endthereof, a second electrical contact supported for engagement by thefirst-mentionec contact, an elongated bimetallic member having a planari portion adapted to flex relative to said spring in response to changesin temperature, means supporting said bime- 13 cally snap back to itsinitial position upon restoration of said bimetallic member tosubstantially its initial position.

5. An electrical switch comprising an elongated overcenter spring havingintegral central and side portions of different lengths thereby causingsaid spring to snap through a central position upon application of forcethereto, means providing an electrical terminal supporting said springat only one end thereof, means providing an electrical contact on saidspring adjacent the other end thereof, a second electrical contactsupported upon a second terminal member and normally engaged by thefirst-mentioned contact, an elongated bimetallic member having a planarportion adapted to ex relative to said spring in response to changes intemperature, means supporting said bimetallic member in non-stressedcondition and in position for metallic conductive heat exchangerelationship with a surface subject to variations in temperature, motiontransmitting means intermediate said bimetallic member and said springexerting force upon the latter when the said bimetallic member liexesthereby snapping said spring over center to effect separation of saidcontacts, and means engaging the said spring and acting upon the saidcentral portion thereof to limit the movement thereof therebyfacilitating automatic snapping of said spring back to its initialposition upon restoration of said bimetallic member to substantially itsinitial position.

6. An electrical switch comprising a first electrical Contact, anover-center spring, means supporting said spring at only one endthereof, a second electrical contact on said spring adjacent the otherend thereof and movable to and from engagement with the first-mentionedcontact, an elongated planar bimetallic member having its ends slidinglysupported in metal-to-metal heat exchanging relationship with a surfacesubject to temperature variations and with the center of said bimetallicmember free to ex in response to changes in temperature, and motiontransmitting means intermediate the said central portion of saidbimetallic member and said spring, whereby variations in temperature ofsaid surface directly and equally affects both ends of said bimetallicmember causing flexure of the central portion thereof thereby movingsaid second contact relative to said first-mentioned contact.-

7. An electrical switch comprising an over-center spring, meanssupporting said spring at one end thereof, means providing an electricalcontact adjacent the other end of said spring, a resilient arm membersupported at one end thereof, a second electrical contact upon 'theother end of said arm member and normally engaged by the first-mentionedContact, an elongated planar bimetallic member having its ends slidinglysupported and its center free to ex in response to changes intemperature, motion transmitting means intermediate the center portionof said bimetallic member and said arm member exerting force upon thelatter when the said bimetallic member flexes thereby snapping saidspring over-center to effect separation of said contacts, and meansoperatively associated with said spring causing the latter to snap backto its initial position upon restoration of said bimetallic member tosubstantially its initial position.

8. An electrical switch comprising a rigid supporting membersubstantially U-shaped in longitudinal cross section with integraloutwardly extending flanges at the ends of the side portions thereof, afirst electrical contact supported on said member, an over-centerspring, means supporting said spring at only one end thereof, a secondelectrical contact carried by said spring adjacent the other end thereoffor movement to and from engagement with the first-mentioned contact,the said supporting member having openings adjacent the flanges thereof,an elongated planar bimetallic member extending transversely of thebight of said U-shaped supporting member with the end portions of saidbimetallic member extending through the openings of said supportingmember and slidably supported upon the said flanges thereof, the centralportion of said bimetallic member being free to deect in response tovariations in temperature, and motion transmitting means intermediatethe central portion of said bimetallic member and the said spring toeffect movement thereof.

9. An electrical switch comprising a rigid supporting member, anelongated over-center spring supported at one end upon said supportingmember, a resilient arm member supported adjacent one end upon saidsupporting member and extending adjacent said spring with the saidspring and arm member normally in engagement adjacent the ends thereofopposite the supported ends thereof thereby providing a normally closedcircuit therebetween, an elongated panar bimetallic member having itsends slidingly supported on said supporting member and its centralportion free to deflect in response to variations in temperature, motiontransmitting means intermediate the central portion of said bimetallicmember and the central portion of said arm member exerting force uponthe latter to snap the said spring through center and thus effectopening of said circuit, and means for applying a spring resetting forcefrom said arm member to said spring upon restoration of said bimetallicmember to substantially its initial position.

10. An electrical switch comprising a rigid supporting member, anelectrical terminal member insulatingly mounted on said supportingmember, an elongated overcenter spring supported at one end by saidterminal member, the said spring having a central portion of greaterlength than the sides thereof thereby causing said spring to snapthrough a central position upon application of force thereto, a secondterminal member insulatingly mounted on said supporting member, aresilient arm member supported by said second terminal member andextending adjacent said spring with the said spring and arm membernormally in engagement adjacent the ends thereof opposite the saidterminal members thereby providing a normally closed circuit between thesaid terminal members, an elongated planar bimetallic member having itsends slidingly supported on said supporting member' and its centralportion free to deflect in response to variations in temperature, motiontransmitting means intermediate the central portion of said bimetallicmember and the central portion of said arm member exerting force uponthe latter to snap the spring through center and thus effect opening ofsaid circuit upon deection of said bimetallic member, and means bearingupon the central portion of said spring facilitating snapping of thelatter back to its initial position upon restoration of said bimetallicmember to substantially its initial position.

11. An electrical switch comprising a rigid supporting member, anelongated over-center spring supported at one end upon said supportingmember, a resilient arm member supported at one end upon said supportingmember and extending in spaced parallel relationship with said springand with the said spring and resilient arm member normally in engagementadjacent the ends thereof opposite the supported ends thereof therebyproviding a normally closed circuit therebetween, an elongated planarbimetallic member having its ends slidingly supported on said supportingmember and its central portion free to deflect in response to variationsin temperature, motion transmitting means intermediate the centralportion of said bimetallic member and the central portion of said armmember exerting force upon the latter and through the latter upon saidspring adjacent the unsupported end thereof to snap the latter throughcenter and thus effect opening of said circuit when said bimetallicmember deects, means for applying a spring resetting force from said armmember to said spring upon restoration of said bimetallic member tosubstantially its initial position, and means bearing upon the centralportion t said spring on the same side thereof as that which is engagedby said arm facilitating the snapping of said spring back to its initialposition.

12. An electrical switch as defined in claim l1 and further comprisingmeans movably mounted on said supporting member and adjustable towardsand away from the said spring on the side thereof opposite the saidmeans bearing upon the central portion of said spring to thereby adjustthe operation of said switch.

13. An electrical switch comprising an over-center spring, meanssupporting said spring only at one end thereof, means providing anelectrical contact on said spring adjacent the other end thereof, an armmember supported at one end thereof, an electrical contact on the otherend of said arm member adapted to be engaged by the first-mentionedcontact, an elongated planar bimetallic member having its ends slidinglysupported and its central portion free to flex in response to changes intemperature, means on the central portion of said bimetallic memberengaging the central portion of said spring thereby exerting force uponthe latter causing said spring to snap through center and effectmovement of the contact thereon relative to the Contact on said armmember upon lexing of said bimetallic member, and means acting upon saidspring to automatically restore the latter to its initial position uponrestoration of said bimetallic member to substantially its initialposition.

14. An electrical switch comprising a rigid supporting member, anover-center spring mounted at one end upon said supporting member, anarm member mounted at one end on said supporting member and extending inparallel spaced relationship with said spring with the outer ends ofsaid spring and arm member normally in engagement, an elongatedbimetallic member having its ends slidable upon said supporting memberand its central portion free to flex, means on the central portion ofsaid bimetallic member engaging said spring adjacent the central portionthereof thereby causing the said spring to snap through center andeffect separation between the spring and the arm member upon apredetermined extent of flexing of said bimetallic member, and an armmember engaging the central portion of said spring on the side thereofopposite said bimetallic member and exerting force on said spring in adirection causing snapping of the spring back to its original positionupon restoration of said bimetallic member to substantially its initialposition.

l5. An electrical switch comprising a rigid supporting member, anelongated over-center spring mounted at one end upon said supportingmember, the said spring having a`y central portion of greater lengththan the sides thereof thereby causing said spring to snap through acentral position upon application of force thereto, an arm membermounted at one end on said supporting member and extending in parallelspaced relationship with said spring with the outer ends of said springand arm member normally in engagement, an elongated bimetallic memberhaving its ends slidably supported upon said supporting member and thecentral portion free to Hex, means on the central portion of saidbitnetallic member engaging said spring adjacent the central portionthereof thereby exerting force thereon causing the said spring to snapthrough center and effect separation between the spring and the arrnmember upon a predetermined flexing of said bimetallic member, meanslimiting the extent of movement of said spring, means causing snappingof said spring back to its original position upon restoration of saidbimetallic member to substantially its initial position, and adjustablemeans engaging said arm member to adjust said switch for operation atdifferent predetermined temperatures.

i6. An electrical switch comprising a rigid supporting member, a lirstterminal member insulatingly mounted upon said supporting member, anelongated over-center spring connected at one end with said terminalmember, the said spring having integral central and side portions ofdifferent lengths thereby causing said spring to snap through a centralposition upon application of force thereto, a second terminal memberinsulatingly connected with said supporting member adjacent theiirst-mentioned terminal member, an arm member connected with saidsecond terminal member and extending in parallel spaced relationshipwith said spring with the outer ends of said spring and arm membernormally in engagement, an elongated bimetallic member having its endsslidably' supported upon said supporting member and the central portionfree to flex, means on the central portion of said bimetallic memberengaging said spring adjacent the central portion thereof therebyexerting force thereon causing the said spring to snap through centerand effect separation between the spring and the arm member upon apredetermined flexing of said bimetallic member, means limiting theextent of movement of said spring, means applying a resetting force tosaid spring upon restoration of said bimetallic member to substantiallyits initial position, and adjustable means movably mounted on saidsupporting member and engaging said arm member to thereby adjust theoperation of said switch.

17. An electrical switch comprising an over-center spring, meanssupporting said spring at one end thereof, an electrical contact mountedin spaced relationship with respect to the supporting means for saispring and adapted to be engaged by the free end of said spring, a leverpivoted adjacent one end and having its other end positioned forengagement with said spring to exert force thereon in a direction tocause the latter to snap through center in one direction thereby movingthe free end thereof from engagement with said contact, means positionedon the opposite side of said spring from said lever and acting upon saidspring to snap the latter through center in the opposite direction uponrelease of the force exerted by said lover, an elongated planarbimetallic member having a portion thereof free to flex in response tochanges in temperature, and motion transmitting means intermediate thesaid portion of the bimetallic member and the said lever to exert switchoperating force thereon upon a predetermined Variation in temperature.

18. An electrical switch as dened in claim 17 and further cornprisingmeans to adju-st the pivot of said lever to thereby adjust said switchfor operation at different predetermined temperatures.

19. An electrical switch comprising an elongated overcenter springhaving a central portion of greater length than the sides thereofthereby causing said spring to snap through a central position uponapplication of force thereto, means providing an electrical terminalsupporting said spring at one end thereof, a second electrical terminalmounted in spaced relationship with respect to said first terminal andhaving a portion adapted to be engaged by the free end of said spring, alever pivoted adjacent one end and having its other end positioned forengagement with said spring to exert force thereon in a direction tocause the latter to snap through center in one direction thereby movingthe free end thereof from engagement with said second terminal, a rigidarm positioned on the opposite side of said spring from said lever andacting upon said spring to snap the latter through center in theopposite direction upon release of the force exerted by said lever, anelongated planar bimetallic member having its ends slidably supportedand its central portion free to flex in response to changes intemperature, and motion transmitting means intermediate the centralportion of said bimetallic member and the said lever to thereby exertswitch Operating force thereon upon a predetermined variation intemperature.

20. An electrical switch comprising an over-center spring, meanssupporting said spring only at one end thereof, an electrical contactmounted in spaced relationship with respect to supporting means for saidspring and adapted to be engaged by the free end of said spring, anelongated planar bimetallic member supported at one end with its otherend unsupported and free to ilex in response to a predetermined changein temperature thereby exerting force upon said spring in a directioncausing the latter to snap through center in one direction thus movingthe free end of the spring from engagement with said contact, andsubstantially rigid means positioned on the opposite side of said springfrom the bimetallic member and acting upon said spring to automaticallysnap the latter through center in the opposite direction upon release ofthe force exerted by said bimetallic member.

2l. An electrical switch comprising an over-center spring havingintegral central and side portions of different lengths thereby causingsaid spring to snap through a central position upon application of forcethereto, means supporting said spring only at one end thereof, anelectrical contact mounted in spaced relationship with respect to saidspring supporting means and adapted to be engaged by the free end ofsaid spring, an elongated planar bimetallic member supported at one endwith its other end unsupported and free to Hex in response to apredetermined change in temperature for exerting force upon the centralportion of said spring in a direction causing the spring to snap throughcenter in one direction thereby moving the free end thereof fromengagement with said contact, and a substantially rigid arm positionedon the opposite side of said spring from the bimetallic member andacting upon said spring to automatically snap the latter through centerin the opposite direction upon release of the force exerted by saidbimetallic member.

22. An electrical switch comprising an over-center spring, meansproviding an electrical terminal supporting said spring only at one endthereof, a second electrical terminal mounted in spaced relationshipwith respect to said first terminal and having a portion adapted to beengaged by the free end of said spring, an elongated planar bimetallicmember supported at one end with its other end unsupported and free toex in response to a predetermined change in temperature thereby exertingforce upon said spring in a direction causing the latter to snap throughcenter in one direction thus moving the free end of the spring fromengagement with said second terminal, substantially rigid meanspositioned on the opposite side of said spring from the bimetallicmember and acting upon said spring to automatically snap the latterthrough center in the opposite direction upon release of the forceexerted by said bimetallic member, and settable means engaging saidbimetallic member intermediate its ends to thereby adjust Said switchfor operation at different predetermined temperatures.

23. An electrical switch comprising an over-center spring, meanssupporting said spring at only one end thereof, means providing anelectrical contact adjacent the other end of said spring, a resilientarm member supported at one end thereof, a second electrical contactupon the other end of said arm member and normally engaged by thefirst-mentioned contact, an elongated bimetallic member supported innon-stressed condition and in good heat exchanging relationship with asurface subject to variation in temperature and having a planar portionfree to ilex in response to changes in temperature, motion transmittingmeans intermediate the planar portion of said bimetallic member and saidarm member exerting force upon the latter when the said bimetallicmember exes thereby snapping said spring over-center to effectseparation of said contacts, and means operatively associated with saidspring and acting thereon to cause the latter to automatically snap backto its initial position upon restoration of said bimetallic member tosubstantially its initial position.

24. An electrical switch comprising an over-center spring, meanssupporting said spring only at one end thereof, means providing anelectrical contact on said spring adjacent the other end thereof, an armmember supported on one end thereof, means providing an electricalcontact on the other end of said arm member and adapted to be engaged bythe rst-mentioned contact, an elongated planar bimetallic member havingits ends slidingly supported and its central portion free to flex inresponse to changes in temperature, and means on the central portion ofsaid bimetallic member engaging the center portion of said spring,thereby exerting force on the latter causing the said spring to snapthrough center and elect movement of the contact thereon relative to thecontact on said arm member upon exing of said bimetallic member.

References Cited in the le of this patent UNITED STATES PATENTS1,668,974 Mottlau May 8, 1928 1,733,085 Thomas Oct. 22, 1929 2,027,118Prosser Ian. 7, 1936 2,289,061 Mertler July 7, 1942 2,394,121 UlanetFeb. 5, 1946 2,521,015 McLaren et al Sept. 5, 1950 2,616,996 Beeman Nov.4, 1952

